This invention relates to the detection of small ionic concentrations of impurities in electrolytic fluids using electrical resistance measurement of electrolytic membranes, and additionally, to the application of such detection to the field of chemical warfare agent presence sensing.
The present day living and working environment exposes humans to a variety of gaseous vapor and liquids, some of which are of known toxicity or pose other health consequences and, are therefore, of intense concern regarding exposure dosage level and environmental presence. The organophosphorous pesticides and the structurally related chemical warfare agents are a particularly important group of potential environmental contaminates. The organophosphorous compounds and similar compounds involving the elements, chlorine, sulfur and flourine, are somewhat unique among environmental contaminants in that they are intentionally synthesized and have economic value which is based on their effect on living organisms and upon their time persistence. The presence of such compounds and the possibility of their accidental or intentional contamination of water supply systems and other environmental resources needed for life support motivates an intense need for monitoring and measuring instrumentation capable of responding to small concentrations of such materials.
Presently available water pollution monitoring instrumentation, for example, varies widely in its achieved measurement accuracy and its portability. A high accuracy but low portability water monitoring function can be accomplished by transporting samples to a central and well-equipped laboratory at one end of the monitoring spectrum, and also by the use of portable analytic instruments carried to the location of possibly contaminated water at the other end of this spectrum. The arrangement of the present invention offers a desirable intermediate capability that lies between these two extremes of the monitoring spectrum in the form of a reasonable small and portable and accurate instrument which is also low in cost and reasonable simple to operate and maintain.
The present monitoring system is based on the use of ion selective membranes. Previous considerations of ion selective membranes include an investigation and technical journal article written by J. H. B. George and R. A. Courant, titled "Conductance and Water Transfer in a Leached Cation-Exchange Membrane", which was published in the Journal of Physical Chemistry, Volume 71, page 246, January 1967, and describes the phenomenon of conductance in membrane structures for a variety of materials including alkaline metals and alkaline earths. The properties of ion exchange membranes in the presence of sodium chloride in solution is described in the article "Electrostatic Phenomena in Ion Exchange Membranes" written by S. D'Allessandro and A. Tantillo, appearing at Volume 9, page 225 in the journal "Desalination," a publication from The Netherlands, published in 1971. An early article regarding ion conductivity appeared in the journal "Z. Electrochem," a publication from West Germany, Volume 55, No. 6, page 475, August 1951, and was authored by J. Mancke and K. F. Bonhoeffer. The disclosure of these publications is hereby incorporated by reference into the present document.
As indicated by these publications, the use of ion selective diffusion membranes for certain purposes is known in the art. The use of such membranes for sensing ions of the type considered in the present invention has not been considered in the prior art however.